1. Field of the Invention
The present invention relates to an apparatus using a disc-shaped record bearing medium having at least one rotation indication portion.
2. Description of the Prior Art
It is important for a recording and/or reproducing apparatus of the kind performing information recording or reproduction on or from such a record bearing medium as a rotary magnetic recording disc or the like to accurately and firmly mount the record bearing medium on a rotating driving shaft of the apparatus in such a manner as to avoid eccentricity of the medium relative to the driving shaft. Inaccurate mounting of the record bearing medium on the rotating driving shaft creates problems in that a recording or reproducing head of the apparatus inadequately contacts the record bearing medium, for example, due to an increase in spacing loss and in that the head deviates from recording tracks to degrade the reproducing characteristic of the apparatus due to the eccentricity.
To accurately mount the record bearing medium on the rotation driving shaft, therefore, there has been proposed a method of mounting the medium via a center core by arranging it in the middle part thereof. The center core is made of a plastic material and is arranged as a reinforcement member to receive and hold the driving shaft of the apparatus at the center of rotation of the record bearing medium which may be a magnetic disc. The center core is provided with a driving shaft inserting hole. The inserting hole is provided with positioning surfaces which are arranged to make the center of rotation of the medium coincide with that of the driving shaft and an elastic part which is arranged to push the driving shaft against these positioning surfaces. This method, however, necessitates arrangement of some means for pressing the center core onto the driving shaft to accurately and reliably mount the record bearing medium on the rotating driving shaft. In that instance, it is conceivable to allow the pressing means to rotate together with the driving shaft after mounting of the record bearing medium. Such arrangement, however, results in an increased inertia of the rotation system. Then, this either results in an increased size of the rotation drive source or a degradation of rotation accuracy. To avoid inconvenience, the abovestated pressing means is preferably arranged to be retractable immediately after completion of mounting of the record bearing medium.
Meanwhile, in cases where the signal such as a video signal to be recorded on the record bearing medium and the rotation of the record bearing medium must be synchronized with each other in phase, it becomes necessary to provide the record bearing medium with phase indicating means such as a magnetic pin and to detect the rotation phase of the record bearing medium by phase detecting means (magnetic pick-up means). In such a case, however, the phase detecting means must be arranged to be close to a rotating part. This requirement then further complicates the structural arrangement of the apparatus.